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Wire temperature control

Discussion in 'General Electronics Discussion' started by alexis damianidis, May 17, 2015.

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  1. alexis damianidis

    alexis damianidis

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    May 17, 2015
    Hey,
    I would like to know how I can determine and control the temperature of a wire at a specific point of temperature.
    I want to control the temperature from 100 to 300 celcius.
    I have an MOSFET and is controller by an MCU.It will be able to variably change the voltage and increase the temperature of the wire.I just do notr know how I can control the temperatute to certain values from 100c to 300c
    Is there any algorithm?
    I am thinking of using a ni200 nickelium wire
     
  2. hevans1944

    hevans1944 Hop - AC8NS

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    Jun 21, 2012
    Welcome to Electronics Point!

    Can you provide some details of what you are trying to do? There are many ways to sense temperature, some more practical than others.

    I would suggest you measure the resistance of the wire at several temperatures between 100 and 300 C using an oven and an accurate thermometer. Then plot the resistance versus temperature on a graph and fill in the blanks by fitting a curve to the data points. You can use this information to build a look-up table that translates resistance to temperature, or try to fit an analytical curve to the data and use the equation for that curve to relate wire resistance to wire temperature. You will need to measure the current and the voltage drop across the wire with the MCU to calculate the resistance and from that the temperature. I would suggest using the MCU to control the current (constant current drive), increasing or decreasing according to whether the wire temperature is too low or too high.

    There are many temperature control algorithms, but PID is traditionally used as a starting point. I would start with a simple proportional controller (the P part of PID) and go from there. A lot will depend on how accurate you need to control the temperature, the amount of power available to heat the wire, the amount of heat loss and thermal mass the wire sees as a thermal load. Please provide details of your application. Are you building a vape?

    Hop
     
  3. Harald Kapp

    Harald Kapp Moderator Moderator

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    Nov 17, 2011
    Welcome to electronicspoint.

    Many. Which one to use depends on the accuracy that you need.

    The most simple algorithm is to apply a defined power for each temperature setting. This will be rather inaccurate as this method does not account for heat energy lost from the wire due to e.g. radiation or heat transfer to another object.

    Another method requires to sense the temperature of the wire. Turn on power if the temperature is lower than the setpoint, turn off power if the emperature is higher than the setpoint. This is what a typical thermostat ofr your appartment heating does (bang-bang control).

    From there on you can make the control algorithm more and more sophisticated, e.g. use a PID controller (which requires some tning to work correctly).

    As a note on the side: As a wire is thermally slow (change of temperature with power), I suggest you use pulse width modulation (PWM) to control the amount of power to the wire.
     
    Last edited: May 18, 2015
  4. poor mystic

    poor mystic

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    Apr 8, 2011
    All good suggestions I am sure.
    On the hardware side, I suggest that switching the MOSFET fully on and fully off many times per second, with a variable duty cycle, would be a much better way to control the power dissipated in the heating resistor than having your transistor switched half-on, half off in a variable resistance mode.
     
    hevans1944 likes this.
  5. Harald Kapp

    Harald Kapp Moderator Moderator

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    Nov 17, 2011
    That's what PWM is all about.
     
  6. HellasTechn

    HellasTechn

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    Apr 14, 2013
    Πατριώτη !

    Welcome. It is always a good idea to provide a little more information about what you want to do in order to get proper assistance :)
     
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